System and method having improved efficiency and reliability for distributing a file among a plurality of recipients

ABSTRACT

A reliable system and method for distributing a file from a first node to a plurality of recipient nodes is provided. The method comprises attempting to distribute a plurality of subfiles that comprise a file from a first node to a first group comprising a plurality of recipient nodes, wherein the first node attempts to distribute at least one subfile to each recipient node of the first group but not all of the plurality of subfiles are distributed from the first node to any of the recipient nodes of the first group. The method further comprises detecting whether one of the plurality of recipient nodes of the first group has failed, and if a recipient node of the first group has failed, managing the distribution of the plurality of subfiles to detour their distribution around the failed node such that the file is distributed to each non-failed node of the plurality of recipient nodes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to concurrently filed and commonly assigned U.S. patent application Ser. No. ______ [Attorney Docket No. 200310234-1] titled “SYSTEM AND METHOD HAVING IMPROVED EFFICIENCY FOR DISTRIBUTING A FILE AMONG A PLURALITY OF RECIPIENTS”, the disclosure of which is hereby incorporated herein by reference. This application is also related to co-pending and commonly assigned-U.S. patent application Ser. No. 10/345,716, filed Jan. 16, 2003, titled “SYSTEM AND METHOD FOR EFFICIENTLY REPLICATING A FILE AMONG A PLURALITY OF RECIPIENTS”, co-pending and commonly assigned U.S. patent application Ser. No. 10/345,587; filed January. 16, 2003, titled “SYSTEM AND METHOD FOR EFFICIENTLY REPLICATING A FILE AMONG A PLURALITY OF RECIPIENTS IN A RELIABLE MANNER”, co-pending and commonly assigned U.S. patent application Ser. No. 10,345,718, filed Jan. 16, 2003, titled “SYSTEM AND METHOD FOR EFFICIENTLY REPLICATING A FILE AMONG A PLURALITY OF RECIPIENTS HAVING IMPROVED SCALABILITY”, co-pending and commonly assigned U.S. patent application Ser. No. 10/345,719, filed Jan. 16, 2003, titled “SYSTEM AND METHOD FOR EFFICIENTLY REPLICATING A FILE AMONG A PLURALITY OF RECIPIENTS HAVING IMPROVED SCALABILITY AND RELIABILITY”, and co-pending and commonly assigned U.S. patent application Ser. No. 10/429,797, filed May 5, 2003, titled “SYSTEM AND METHOD FOR EFFICIENT REPLICATION OF FILES ENCODED WITH MULTIPLE DESCRIPTION CODING”, the disclosures of which are hereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates in general to file distribution, and more specifically to systems and methods for efficiently distributing a file from a first node to a plurality of recipient nodes in a scalable and reliable manner that accounts for node failures.

DESCRIPTION OF RELATED ART

Today, much information is stored as digital data. Such information is often available to processor-based devices via client-server networks. Client-server networks are delivering a large array of information (including content and services) such as news, entertainment, personal shopping, airline reservations, rental car reservations, hotel reservations, on-line auctions, on-line banking, stock market trading, as well as many other services and types of content. Such information providers (sometimes referred to as “content providers”) are making an ever-increasing amount of information available to users via client-server networks.

It is often desirable to communicate information to a plurality of different recipients. More particularly, it is often desirable to replicate a large file among a number of distributed computers. For instance, in some situations it is desirable for a plurality of distributed clients to receive a replicated file. For example, suppose a number of client computers comprise a software application program, and the application program's provider makes a modification or update to the program. The application provider may desire to distribute the software update to each of the client computers. As another example, a company may receive a new software program and desire to distribute the software program to all of its computers that are communicatively coupled to the company's Local Area Network (LAN) or Intranet.

As still another example, it may be desirable for a large file to be replicated among a plurality of distributed servers. For instance, as described further below, a plurality of distributed servers may be established for efficiently serving content to clients (e.g., each server may be responsible for a particular geographical region of clients), and it may be desirable to replicate a file from an originating server to the other distributed servers such that all of the servers provide the same content to their respective clients. For example, Content Delivery Networks (CDNs) are based on a large-scale distributed network of servers located closer to the edges of the Internet for efficient delivery of digital content, including various forms of multimedia content. The main goal of the CDN's architecture is to minimize the network impact in the critical path of content delivery as well as to overcome a server overload problem, which is a serious threat for busy sites serving popular content. CDNs implementing distributed content servers are becoming increasingly popular on the Internet, and particularly within the World Wide Web (the “web”) portion of the Internet, for example, for serving content (web documents) to clients. Many edge servers may be implemented within the Internet (e.g., hundreds, thousands, or even hundreds of thousands of edge servers may be implemented) that are each to serve the same, replicated content to their respective clients.

For many web documents (e.g., html pages and images having a relatively small file size) served via CDN, active replication of the original content at the edge servers may not be needed. The CDN's edge servers act as caching servers, and if the requested content is not yet in the cache at the time it is requested by a client, the content is retrieved from the original server using the so-called pull model. The performance penalty associated with the initial document retrieval from the original server to the edge server serving the requesting client, such as higher latency observed by the client and the additional load experienced by the original server, is generally not significant for small to medium size web documents.

For large files (e.g., large documents, software download packages, and media files), a different operational mode is typically preferred. In this case, it is typically desirable to replicate these files at edge servers in advance of a client requesting them, using the so-called push model. For large files, actively replicating the files to a plurality of distributed edge servers is a challenging, resource-intensive problem, e.g., streaming media files can require significant bandwidth and download time due to their large sizes: a 20 minute streaming media file encoded at 1 Mbit/s results in a file of 150 Mbytes. Thus, if such a large file was not actively replicated to the edge servers in advance of a client requesting the file, a significant performance penalty may be incurred for retrieving the file from the original server, such as higher latency observed by the client and the additional load experienced by the original server in providing the large file to the edge server serving the requesting client. Sites supported for efficiency reasons by multiple mirror servers face a similar problem: the original content needs to be replicated across the multiple, geographically distributed, mirror servers.

BRIEF SUMMARY OF THE INVENTION

In certain embodiments of the present invention, a method of distributing a file from a first node to a plurality of recipient nodes is provided. The method comprises partitioning a file F into a plurality of subfiles. The method further includes performing distribution of the file F to a plurality of recipient nodes using a distribution technique that comprises (a) attempting to distribute the plurality of sub files from a first node to a first group of recipient nodes, wherein the first node attempts to communicate at least one subfile to each recipient node of the first group but not all of the plurality of subfiles to any recipient node of the first group, and (b) the plurality of recipient nodes of the first group attempting to exchange their respective sub files received from the first node, wherein at least one recipient node of the first group begins communicating a portion of its respective sub file that it is receiving from the first node to at least one other recipient node of the first group before the at least one recipient node fully receives its respective subfile. The method further comprises detecting a failed node of the plurality of recipient nodes, and the distribution technique adapting to distribute all of the subfiles of the file F to each non-failed node of the plurality of recipient nodes.

In certain embodiments, a system comprises an origin node operable to partition a file F into a plurality of subfiles, wherein the plurality of subfiles correspond in number to a number of recipient nodes in a first group to which the file is to be distributed. The origin node is operable to attempt to distribute all of the plurality of subfiles to the recipient nodes, wherein the origin node attempts to distribute a different one of the plurality of subfiles to each of the recipient nodes. The recipient nodes are operable to attempt to exchange their respective subfiles received from the origin node such that each recipient node obtains all of the plurality of subfiles, wherein at least one recipient node of the first group begins communicating a portion of its respective sub file that it is receiving from the origin node to at least one other recipient node of the first group before the at least one recipient node fully receives its respective subfile from the origin node. The origin node is operable to detect a failed node in the first group, and the origin node is operable to manage distribution of the file F upon detecting a failed node in the first group in a manner such that every non-failed node of the first group receives the file F.

In certain embodiments, a method of distributing a file from a first node to a plurality of recipient nodes comprises attempting to distribute a plurality of subfiles that comprise a file from a first node to a first group comprising a plurality of recipient nodes, wherein the first node attempts to distribute at least one subfile to each recipient node of the first group but not all of the plurality of subfiles are distributed from the first node to any of the recipient nodes of the first group. The method further comprises the plurality of recipient nodes of the first group attempting to exchange their respective subfiles, wherein at least one recipient node of the first group begins communicating a portion of its respective subfile that it is receiving from the first node to at least one other recipient node of the first group before the at least one recipient node fully receives its respective subfile. The method further comprises detecting whether one of the plurality of recipient nodes of the first group has failed, and if a recipient node of the first group has failed, managing the distribution of the plurality of subfiles to detour their distribution around the failed node such that file F is distributed to each non-failed node of the plurality of recipient nodes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example environment in which embodiments of the present invention may be utilized and illustrates an example of distributing subfiles from an origin node to a plurality of recipient nodes in accordance with a file distribution technique of an embodiment of the present invention;

FIG. 2 shows an example of a recipient node communicating the subfile that it received from an origin node to other recipient nodes in accordance with the file distribution technique of FIG. 1;

FIG. 3 shows an example of a recipient node receiving subfiles from each of the other recipient nodes in accordance with the file distribution technique of FIG. 1;

FIG. 4 shows an example of logically arranging a plurality of replication groups of recipient nodes into primary and secondary multicast trees in accordance with an embodiment of the present invention;

FIG. 5 shows an example communication pattern utilized between a first and second replication group of a primary multicast tree in accordance with the example embodiment of FIG. 4;

FIG. 6 shows an example of a fast-forward mode of distribution between replication groups of a primary multicast tree in accordance with the example embodiment of FIG. 4;

FIG. 7 shows the set of communication paths that may be concurrently utilized during the file distribution from an origin node N₀ to a first recipient node N₁ under a file distribution algorithm of one embodiment of the present invention;

FIG. 8 shows an example operational flow diagram for distributing a file from an origin node to a plurality of recipient nodes in accordance with an embodiment of the present invention;

FIG. 9 shows an example repair procedure for a failed node in group Ĝ₁ of primary multicast tree {circumflex over (M)} of FIG. 4;

FIGS. 10A-10C show an example repair procedure for a failed initial node (of group Ĝ₁) of FIG. 4 after such node has fully received its respective subfile from the origin node but before it has forwarded all of such subfile on to the other nodes of the group;

FIGS. 11A-11B show an example repair procedure for a failed subsequent node N_(i) ^(j) in group G_(j); and

FIGS. 12A-12B show an example operational flow diagram for a repair procedure for the example ALM-FastReplica distribution process of FIG. 4 in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

Various embodiments of the present invention are now described with reference to the above figures, wherein like reference numerals represent like parts throughout the several views. As described further below, embodiments of the present invention provide a system and method for distributing a file from a first node (which may be referred to herein as the “origin” node) to a plurality of recipient nodes. In certain embodiments, the plurality of recipient nodes comprise servers, such as edge servers in a CDN or mirror servers as examples. Of course, embodiments of the present invention may also be utilized for distributing a file to client nodes.

According to an embodiment of the present invention, a file distribution technique is provided that is scalable for application in distributing a file to a very large number of recipient nodes. For instance, embodiments of the present invention enable the recipient nodes to be logically organized into a plurality of different groups, with each group having a plurality of recipient nodes, and a file is efficiently distributed to the plurality of groups of recipient nodes.

According to certain embodiments, a file is partitioned into a plurality of parts (or “subfiles”), and the plurality of parts are distributed from the origin node to the recipient nodes. More particularly, all of the subfiles comprising the file to be distributed are communicated from an origin node to the recipient nodes, but the origin node does not send all of the subfiles to each recipient node. That is, the origin node sends only a portion of the subfiles that comprise the file to be distributed to each recipient node. For instance, in one embodiment, each recipient node receives a different one of the subfiles of the file to be distributed.

Further, the recipients exchange their respective subfiles with each other, thus resulting in each recipient obtaining the full file. More specifically, in accordance with embodiments of the present invention, at least one of the recipient nodes begins communicating its respective subfile that it is receiving from the origin node to other recipient nodes before the at least one recipient node receives the full subfile from the origin node. In certain embodiments, the nodes may exchange their respective subfiles in a manner such that they each begin to communicate a portion of their respective subfiles to the other recipient nodes before the full subfile is received from the origin node. Thus, in accordance with embodiments of the present invention, the recipient-nodes may begin communicating portion(s) (e.g., packets) of their respective subfiles to other recipient nodes before their respective subfile is fully received from the origin node.

In view of the above, certain embodiments of the present invention provide a distribution technique in which the origin node is not required to communicate the full file to each recipient node, but rather may communicate only a portion thereof to each recipient node, and the recipient nodes exchange their respective portions to result in each recipient node obtaining all subfiles comprising the full file. Further, the recipient nodes may begin communicating portion(s) (e.g., packets) of their respective subfiles to other recipient nodes before their respective subfiles are fully received from the origin node. That is, the exchange of subfiles between the recipient nodes may be performed concurrently with the communication of the respective subfiles from the origin node to the recipient nodes. Accordingly, an efficient distribution of the file among the plurality of nodes is enabled.

Various techniques may be implemented for distributing a file from an origin node to a plurality of recipient nodes in accordance with embodiments of the present invention. Certain embodiments of the present invention implement a technique referred to herein as the Application-Level Multicast (ALM)-FastReplica distribution technique. With ALM-FastReplica, to replicate a large file F among a total of n recipient nodes, the recipient nodes may be logically grouped into “replication groups” that each have k nodes (or that each have no more than k nodes). As described further below, the value of k may be determined as a function of the maximum number of concurrent communication connections that each node to which the file F is to be distributed can support. The original file F may be partitioned into k subfiles of approximately equal size, and each subfile is communicated from the origin node to a different recipient node of a first replication group. That is, the subfiles are communicated to the recipient nodes of a first replication group from the origin node concurrently. Such communication of the subfiles from the origin node to the recipient nodes is referred to herein as a “distribution” step.

Further, each recipient node propagates its respective subfile (i.e., the subfile that it receives from the origin node) to the remaining recipient nodes of its respective replication group. That is, each recipient node concurrently communicates its subfile to the other nodes of the replication group. This exchange of subfiles by recipient nodes is referred to herein as a “collection” step, as the recipient nodes of a replication group each collect the subfiles comprising file F from the other recipient nodes of the replication group. In accordance with embodiments of the present invention, the recipient nodes may begin communicating portion(s) of their respective subfiles to other recipient nodes before the entire subfile is received from the origin node. For instance, a first recipient node may receive a first subfile F, of file F from an origin node, and such first recipient node may communicate the first subfile F, to other recipient nodes of its respective replication group. Such first recipient node may begin communicating the first subfile F, to other recipient nodes of its respective replication group before the first recipient node receives all of the first subfile F, from the origin node. For example, while the first recipient node has a communication connection established with the origin node, through which the first recipient node is receiving packets of subfile F₁, the first recipient node may establish concurrent communication connections to the other recipient nodes of its respective replication group and begin communicating the received packets of subfile F₁ to the other recipient nodes before all packets of subfile F₁ are received by the first recipient node. In certain embodiments, the first recipient node may forward the packets of subfile F₁ to the other nodes of its replication group as the packets are received by the first recipient node from the origin node. Thus, the above-described distribution and collection steps may effectively be performed concurrently in certain embodiments of the present invention. Additionally, as described further below, if there is more than one replication group, the file may be further communicated to other replication groups. In certain embodiments, a recipient node of a first replication group may begin communicating a subfile that it is receiving from an origin node to a recipient node of a second replication group before the recipient node of the first replication group receives the full subfile from the origin node.

Embodiments of the present invention improve the robustness (or “reliability”) of the above file distribution process to deal with node failures. As can be seen from the above description of ALM-FastReplica, for example, such ALM-FastReplica algorithm is sensitive to node failures. For example, if a node of a group fails during the collection step for the group, this event may impact all other nodes in such distribution group because each node depends on the other nodes of the group to receive the other nodes' respective subfiles. Embodiments of the present invention enable reliable distribution of a file to recipient nodes even if node failures are encountered. More particularly, techniques for detecting a node failure and detouring the distribution of the subfiles around such failed node are provided in an embodiment of the present invention.

To better appreciate aspects of embodiments of the present invention, it is appropriate to briefly review the existing techniques in the art for file distribution. Currently, the three most popular methods used for content distribution (or file “replication”) in the Internet environment are: (1) satellite distribution, (2) multicast distribution, and (3) application-level multicast distribution.

With satellite distribution, the content distribution server (or the “origin node”) has a transmitting antenna. The servers (or “recipient nodes”) to which the content should be replicated (or the corresponding Internet Data centers, where the servers are located) have a satellite receiving dish. The original content distribution server broadcasts a file via a satellite channel. Among the shortcomings of the satellite distribution method are that it requires special hardware deployment and the supporting infrastructure (or service) is quite expensive.

With multicast distribution, such as “IP Multicast” distribution, an application can send one copy of each packet of a file and address it to the group of recipient nodes (IP addresses) that want to receive it. This technique reduces network traffic by simultaneously delivering a single stream of information to hundreds/thousands of interested recipients. Multicast can be implemented at both the data-link layer and the network layer. Applications that take advantage of multicast technologies include video conferencing, corporate communications, distance learning, and distribution of software, stock quotes, and news. Among the shortcomings of the multicast distribution method is that it requires a multicast support in routers, which still is not consistently available across the Internet infrastructure.

Since the native IP multicast has not received widespread deployment, many industrial and research efforts have shifted to investigating and deploying “application-level multicast,” where nodes across the Internet act as intermediate routers to efficiently distribute content along a predefined mesh or tree. A growing number of researchers have advocated this alternative approach, where all multicast related functionality, including group management and packet replication, is implemented at end systems. In this architecture, nodes participating in the multicast group self-organize themselves into a scalable overlay structure using a distributed protocol. Further, the nodes attempt to optimize the efficiency of the overlay by adapting to changing network conditions and considering the application-level requirements.

An extension for the end-system multicast is introduced by J. Byers, J. Considine, and M. Mitzenmacher in “Informed Content Delivery Across Adaptive Overlay Networks”, Proc. Of ACM SIGCOMM, 2002, in which instead of using the end systems as routers forwarding the packets, the authors propose that the end-systems actively collaborate in an informed manner to improve the performance of large file distribution. The main idea is to overcome the limitation of the traditional service models based on tree topologies where the transfer rate to the client is defined by the bandwidth of the bottleneck link of the communication path from the origin server. The authors propose to use additional cross-connections between the end-systems to exchange the complementary content these nodes have already received. Assuming that any given pair of end-systems has not received exactly the same content, these cross-connections between the end-systems can be used to “reconcile” the differences in received content in order to reduce the total transfer time.

As mentioned above, certain embodiments of the present invention may implement a distribution technique referred to herein as the ALM-FastReplica distribution technique. As with the above-described application-level multicast approaches proposed in the existing art, implementations of such ALM-FastReplica distribution technique use the end nodes for packet replication. In accordance with embodiments of the present invention, the ALM-FastReplica distribution technique provides a technique for efficiently distributing a file among a plurality of nodes (e.g., by distributing a file in a manner that efficiently utilizes communication paths available between the nodes). Example embodiments implementing such ALM-FastReplica technique are described further below.

Consider the following notations:

-   -   (a) Let N₀ be a node (which may be referred to as an “origin         node” or “origin server”) which has an original file F, and let         Size(F) denote the size of file F in bytes; and     -   (b) Let R={N₁, . . . , N_(m)} be a replication set of nodes         (i.e., a set of recipient nodes to which the file F is to be         distributed).         The problem becomes replicating file F across nodes N₁, . . . ,         N_(n), while minimizing the overall replication time.

In accordance with certain embodiments, let k be a function of the maximum number of concurrent connections that each node can support. As an example, in one embodiment described further below, k is equal to the maximum number of concurrent connections that each node can support (which is typically 30 or less). In another example embodiment described further below, k+1 is the maximum number of concurrent connections that each node can support. In a further example embodiment described below, k+2 is the maximum number of concurrent connections that each node can support. Thus, in certain embodiments, k may be a number of network connections chosen for concurrent transfers between a single node and multiple recipient nodes. If n>k, then the original set R of n nodes to which file F is to be distributed are partitioned into-replication groups that each have k nodes. Further, file F is divided into k subsequent subfiles {F₁, . . . , F_(k)} that are each approximately of equal size.

In one implementation of this ALM-FastReplica technique, file F is divided into k equal subsequent subfiles: F₁, . . . , F_(k), where ${{Size}\left( F_{i} \right)} = \frac{{Size}(F)}{k}$ bytes for each i: 1≦i≦k. The ALM-FastReplica algorithm then performs a distribution step in which origin node N₀ opens k concurrent network connections to nodes N₁, . . . , N_(k) of a first replication group, and sends to each recipient node N_(i) (1≦i≦k) the following items:

-   -   (a) a distribution list of nodes R={N₁, . . . , N_(k)} to which         subfile F_(i) is to be sent during the collection step (each         node N_(i) is itself excluded from its distribution list); and     -   (b) subfile F_(i).

An example of this distribution step of the ALM-FastReplica algorithm is shown in FIG. 1. For instance, FIG. 1 shows an example environment 100 in which embodiments of the present invention may be utilized. Environment 100 comprises origin node N₀ and recipient nodes N₁, N₂, N₃, . . . , N_(k−1), N_(k) that are communicatively coupled via communication network 101. Communication network 101 is preferably a packet-switched network, and in various implementations may comprise, as examples, the Internet or other Wide Area Network (WAN), an Intranet, Local Area Network (LAN), wireless network, Public (or private) Switched Telephony Network (PSTN), a combination of the above, or any other communications network now known or later developed within the networking arts that permits two or more computing devices to communicate with each other. In certain embodiments, nodes N₀-N_(k) comprise server computers. For instance, nodes N₁, . . . , N_(k) may comprise edge servers in a CDN or mirror servers within a mirrored network. In other embodiments, nodes N₀-N_(k) may comprise server and/or client computers. For example, node N₀ may comprise a server computer, and nodes N₁, . . . , N_(k) may comprise client computers to receive a file (e.g., software application file, etc.) from node N₀.

Origin node N₀ comprises file F stored thereto, and such file F is partitioned into k subfiles F₁, F₂, F₃, . . . , F_(k−1), F_(k), wherein the sum of subfiles F₁, F₂, F₃, . . . , F_(k−1), F_(k) comprises the total file F. As shown, the plurality of subfiles are distributed from origin node N₀ to the recipient nodes N₁, . . . , N_(k). More particularly, all of the k subfiles comprising file F are communicated from origin node N₀ to the recipient nodes N₁, . . . , N_(k), but origin node N₀ does not send all of the k sub files to each recipient node. That is, origin node N₀ sends only a portion of the k subfiles to each recipient node. For instance, in this example, each recipient node receives a different one of the k subfiles from origin node N₀. More particularly, origin node N₀ communicates subfile F₁ to node N₁, subfile F₂ to node N₂, subfile F₃ to node N₃, . . . , subfile F_(k−1) to node N_(k−1), and subfile F_(k) to node N_(k) via communication network 101. Additionally, in an embodiment of the present invention, origin node N₀ also sends a distribution list to each recipient node N₁, . . . , N_(k). The distribution list for each node identifies the other recipient nodes that such recipient node is to communicate the subfile that it receives from origin node N₀. For example, origin node N₀ may send to node N₁ a distribution list identifying nodes N₂, . . . , N_(k). Similarly, origin node N₀ may send to node N₂ a distribution list identifying nodes N₁, and N₃, . . . , N_(k), and soon.

The ALM-FastReplica algorithm also performs a collection step. An example of the collection step is described herein in conjunction with FIGS. 2 and 3. After receiving at least a portion of file F_(i) (e.g., at least a first packet thereof), node Ns opens (k−1) concurrent network connections to remaining nodes in the recipient group and sends the received portion of subfile F_(i) to them, as shown in FIG. 2 for node N₁. More particularly, FIG. 2 shows that node N₁ opens k−1 concurrent network connections, i.e., one network connection with each of recipient nodes N₂, . . . , N_(k) Node N₁ communicates subfile F₁, which it receives from origin node N₀ in the above-described distribution step, to each of the recipient nodes N₂, . . . , N_(k). As described further below, node N₁ may begin communicating a portion of subfile F₁ to the other recipient nodes N₂, . . . , N_(k) before node N₁ receives all of subfile F, from origin node N₀. For instance, when implemented in a packet-switched network, node N₁ may begin communicating packets of subfile F₁ to the other recipient nodes N₂, . . . , N_(k) before node N₁ receives all packets of subfile F₁ from origin node N₀. In certain implementations, node N₁ may communicate packets of subfile F, to the other recipient nodes N₂, . . . , N_(k) as those packets are received by node N₁ from origin node N₀.

Similarly, FIG. 3 shows the set of incoming, concurrent connections to node N₁ from the remaining recipient nodes N₂, . . . , N_(k), transferring the complementary sub files F₂, . . . , F_(k) during the collection step of the ALM-FastReplica algorithm. More particularly, FIG. 3 shows that node N, has k-1 concurrent network connections, i.e., one network connection with each of recipient nodes N₂, . . . , N_(k) through which node N₁ receives the other subfiles comprising file F from the recipient nodes N₂, . . . , N_(k). That is, each of recipient nodes N₂, . . . , N_(k) communicates its respective subfile that it receives from origin node N₀. As described further below, each of nodes N₂, . . . , N_(k) may begin communicating received portions of their respective subfiles, F₂, . . . , F_(k) to the other recipient nodes (e.g., as shown with node N₁ in FIG. 3) before such nodes N₂, . . . , N_(k) receive all of their respective subfile from origin node No. Thus, the distribution step of FIG. 1 and the collection steps of FIGS. 2 and 3 may be effectively performed concurrently.

Accordingly, during the distribution and collection operations, each node N_(i) may have the following set of network connections:

-   -   (a) there are k−1 outgoing connections from node Ni: one         connection to each node N_(i) (j≠i) of the replication group for         sending the corresponding subfile F_(i) to node N_(j); and     -   (b) there are k incoming connections to node N_(i): one         connection from each node N_(j) (j≠i) of the replication group         for sending the corresponding subfile F_(j) to node N_(i) in         addition to the connection from origin node N₀ to node N_(i) for         sending subfile F_(i) to node N_(i).

Thus, at the end of the above distribution and collection operations, each recipient node receives all subfiles F₁, . . . , F_(k) comprising the entire original file F. Accordingly, each of the nodes in the first replication group obtain the full file F (which is reconstructed through the received subfiles). Additionally, if additional replication groups exist, the file nay be further communicated to such additional replication groups (e.g., as described further below) such that the entire set R of recipient nodes n obtain the full file F. An example embodiment of the ALM-FastReplica distribution technique is described further below in conjunction with FIGS. 4-9B.

In accordance with an example embodiment, again let k be a number of network connections chosen for concurrent transfers between a single node and multiple recipient nodes. If the total number of nodes n to which file F is to be distributed is greater than k (i.e., n>k), then the original set R of n nodes are partitioned into replication groups that each have k nodes. Let G₁, . . . , G_(k) ₁ be the corresponding replication groups. Further, file F is divided into k subsequent subfiles {F₁, . . . , F_(k)} that are each approximately of equal size.

Let m be a number of groups comprising a multicast tree. According to previous studies (see e.g., Y. Chu, S. Rao, S. Seshan, H. Z hang, “Enabling conferencing applications on the Internet using an overlay multicast architecture”, Proc. of A CM SIGCOMM, 2001), a reasonable value of m may vary in a range of several 10s of nodes, for example. Then replication groups G₁, . . . , G_(k) may be arranged in the special multicast trees {circumflex over (M)}, M¹, . . . , M^(m) ¹ each having m (or less) groups, where {circumflex over (M)} is referred to as a “primary” multicast tree, and M¹, . . . , M^(m) ¹ are referred to as “secondary” multicast trees. FIG. 4 shows an example of a plurality of replication groups G₁, . . . , G_(k) ₁ that are arranged in such multicast trees {circumflex over (M)}, M¹, . . . , M^(m) ¹ .

A primary multicast tree, {circumflex over (M)}, comprises replication groups in which a portion of a subfile begins being communicated to at least one node thereof from a node of another replication group before the node of such other replication group fully receives the subfile. For instance, in the example of FIG. 4, primary multicast tree {circumflex over (M)} comprises origin node N₀ and replication groups Ĝ₁, Ĝ₂, . . . , Ĝ_(m). At least one recipient node of group Ĝ₁ is operable to begin communicating its respective subfile that it is receiving from origin node N₀ to at least one recipient node of group Ĝ₂ before such at least one node of group Ĝ₁ receives the entire subfile from origin node N₀.

A secondary multicast tree, such as secondary multicast trees M¹, . . . , M^(m) ¹ of the example of FIG. 4, comprises at least one replication group in which a portion of a subfile begins being communicated to a node thereof from a node of another replication group after the node of such other replication group fully receives the subfile. For instance, in the example of FIG. 4, secondary multicast tree M¹ comprises replication groups G₁ ¹, G₂ ¹, . . . , G_(m) ¹. In this example, the recipient nodes of group Ĝ₁ are operable to begin communicating their respective subfiles that they receive from origin node N₀ to at least one recipient node of group G₁ ¹ of secondary tree M¹ after such recipient nodes of group Ĝ₁ fully receive their respective subfiles from origin node N₀. For instance, after a first node of group G, fully receives its respective subfile from origin node N₀, it may terminate its communication connection with origin node N₀ and replace such terminated communication connection with a communication connection to a node of group G₁ ¹ of secondary tree M¹, and the first node may then begin transferring its respective subfile that it received from origin node N₀ to the node of G₁ ¹. The nodes of group G₁ ¹ of secondary tree M¹ may each begin communicating the subfiles that they are receiving from the nodes of group Ĝ₁ to at least one node of a second group G₂ ¹ before fully receiving their respective subfiles. That is, the nodes of group G₁ ¹ of secondary tree M¹ may forward their respective subfiles that they are receiving from the nodes of group Ĝ₁ to the nodes of the next group of the secondary tree M¹, and so on, such that the file F is distributed through the replication groups of the secondary tree in much the same manner as distributed through the primary tree.

To achieve the best performance results, the values m and m₁ (i.e., the number, m, of groups included in each multicast tree versus the number, m₁, of multicast trees) should preferably be similar: this will lead to well-balanced multicast trees. Depending on the number of nodes, n, in the original replication set R, the example ALM-FastReplica algorithm may utilize only a primary multicast tree in certain situations and it may also employ secondary multicast trees in other situations. That is, depending on the number of nodes n to which file F is to be distributed, in certain situations it may be more efficient to utilize only a primary multicast tree, and in other situations it may be more efficient to further utilize secondary multicast trees for the distribution.

In operation, the example ALM-FastReplica algorithm of FIG. 4, first replicates file F via the primary multicast tree {circumflex over (M)}. Once groups Ĝ₁, . . . , Ĝ_(m) comprising the primary multicast tree {circumflex over (M)}, receive subfiles F₁, . . . , F_(k), they initiate (independently from each other) communication of subfiles F₁, . . . , F_(k) to the secondary multicast trees M¹, . . . , M^(m) ¹ .

More specifically, the distribution of file F through the primary multicast tree {circumflex over (M)} in accordance with an example embodiment of the ALM-FastReplica algorithm is as follows. Let groups Ĝ₁, . . . , Ĝ_(m) comprise the primary multicast tree {circumflex over (M)}, as shown in FIG. 4. Let Ĝ₁={N₁ ^(i), . . . , N_(k) ^(i)}, 1≦i≦m. The distribution within the primary multicast tree {circumflex over (M)} of one embodiment comprises performing a distribution step and a collection step, as described below, and it may further comprise a group communication step, as also described below, if more than one replication group is included in the primary multicast tree.

In the distribution step of this example embodiment, originator node N₀ opens k concurrent network connections to nodes N₁ ¹, . . . , N_(k) ¹ of replication group Ĝ₁, and starts sending subfile F_(i) to the corresponding recipient node N_(i) ¹1≦i≦m. This step is represented by box Ĝ₁ (distr) in FIG. 4. In the collection step of this example embodiment, in group Ĝ₁ each node N_(i) ¹, after receiving the first bytes of file F_(i), immediately starts sending the file F_(i) to the rest of the nodes in group Ĝ₁ This type of forwarding in which portions (e.g., packets) of file F_(i) are immediately forwarded from the recipient node to other nodes of a replication group as soon as such portions are received by the recipient node (e.g., from the origin node) may be referred to herein as a “fast-forward” mode of distribution. In this collection step, each node in group Ĝ₁ will be receiving all subfiles F₁, . . . , F_(k) of original file F. This step is represented by box Ĝ₁ (coil) in FIG. 4. It should be understood that while the distribution and collection steps are shown in FIG. 4 as sequential boxes Ĝ₁ (distr) and Ĝ₁ (coll), as described above these operations are effectively performed concurrently.

If, as in the example of FIG. 4, further replication groups exist in the primary multicast tree, then a group communication step is performed in this example embodiment. Thus, for instance, a first replication group, Ĝ₁, distributes file F to a second replication group, Ĝ₂, of the primary multicast tree {circumflex over (M)}. Communication between groups Ĝ₁ and Ĝ₂ follows a different file exchange protocol, defining another communication pattern actively used in this example embodiment of the ALM-FastReplica algorithm. The communication pattern utilized between groups G and 62 in accordance with this example embodiment is shown in FIG. 5. As shown in FIG. 5, each node N_(i) ¹ of group Ĝ₁, after receiving first bytes of subfile F_(i), immediately starts sending the subfile F_(i) to node N_(i) ² of group Ĝ₂. Thus, while the nodes of group Ĝ₁ are performing the distribution and collection steps within such group, each node also concurrently establishes a communication connection to a node of group Ĝ₂. Accordingly, not only does each node of group Ĝ₁ forward the received portions of its respective subfile to the other nodes of group Ĝ₁, but it also forwards the received portions of its respective subfile to a node of group Ĝ₂. That is, before receiving the full subfile from the origin node, a recipient node of group Ĝ₁ begins communicating such subfile to a corresponding node of group Ĝ₂ (in a fast-forward mode of distribution). As shown in FIG. 5, such communication of subfiles from the nodes of group Ĝ₁ to the nodes of group Ĝ₂ is effectively a distribution step.

As further shown in FIG. 5, the nodes of group Ĝ₂ may begin performing the collection step described above, wherein each node N₁ ², N₂ ², . . . , N_(k) ² of group Ĝ₂ opens k−1 concurrent communication connections to the rest of the nodes of group G, for transferring its respective subfile F_(i) (i.e., the subfile that the node received from group Ĝ₁). More specifically, each node of group Ĝ₂ may begin distributing to the other nodes of group Ĝ₂ its respective subfile that it is receiving from a node of group Ĝ₁ before fully receiving such subfile. That is, the nodes of group Ĝ₂ may use a fast-forward mode to perform the collection step concurrently with the distribution step of FIG. 5. In this way, each node of group Ĝ₂ will be receiving all subfiles F₁, . . . , F_(k) of the original file F.

Similarly, group G₂ may start communications with a next group Ĝ₃ (not shown in FIG. 5) using the group communication step immediately after node N_(i) ² receives the first bytes of file F_(i). That is, each node N_(i) ² of group Ĝ₂, after receiving first bytes of subfile F_(i), immediately starts sending the subfile F_(i) to node N_(i) ³ of group Ĝ₃. Thus, while the nodes of group Ĝ₂ are performing the distribution and collection steps within such group, each node also concurrently establishes a communication connection to a node of group G₃. Accordingly, not only does each node of group Ĝ₂ forward the received portions of its respective subfile to the other nodes of group Ĝ₂, but it also forwards the received portions of its respective subfile to a node of group Ĝ₃. This replication procedure continues unrolling through the set of corresponding groups in primary multicast tree {circumflex over (M)} shown in FIG. 4. Thus, the groups of the primary multicast tree {circumflex over (M)} may before group communication in a fast-forward mode of distribution.

An example of such fast-forward distribution between replication groups of a primary multicast tree is shown further in FIG. 6. As shown, the primary multicast tree {circumflex over (M)} is a collection of k multicast sub-trees {circumflex over (M)}_(F) ₁ , {circumflex over (M)}_(F) ₂ , . . . , {circumflex over (M)}_(F) _(k) , where each such sub-tree {circumflex over (M)}_(F) ₁ is replicating the corresponding subfile F_(i). At the same time, nodes from these different multicast sub-trees use additional cross-connections between their nodes (as shown in FIG. 6) to exchange their complementary subfiles.

As shown in FIG. 4, in some implementations, secondary multicast trees may also be utilized for distribution, such as secondary multicast trees M¹, . . . , M^(m) ¹ . Each replication group Ĝ_(i)(1≦i≦m₁) of the primary multicast tree {circumflex over (M)} may initiate the replication process of subfiles F₁, . . . , F_(k) to the next, secondary multicast tree m_(i)={G₁ ^(i), . . . , G_(m) ^(i)} (see FIG. 4). Preferably, these transfers are asynchronous within the group Ĝ_(i)={N₁ ^(i), . . . , N_(k) ^(i)}. When node N_(j) ^(i) receives the entire subfile F_(j) in the primary multicast tree {circumflex over (M)}, it immediately starts transferring subfile F_(j) to group G₁ ^(i) of the secondary tree M^(i) using the group communication step. For example, as shown in FIG. 4, once each node of group Ĝ₁ of primary tree {circumflex over (M)} receives its respective subfile from origin node N₀, such node of group Ĝ₁ may terminate its communication connection with origin node N₀ and replace such communication connection with a connection to a corresponding node of group G₁ ¹ of secondary multicast tree M¹ for communicating its respective subfile that it received from origin node N₀ to the node of group G₁ ¹.

FIG. 7 shows the set of communication paths that may be concurrently utilized during the file distribution from node N₀ to node N₁ under the ALM-FastReplica algorithm (with node N₁ shown as a representative of the recipient nodes). As explained above, during the distribution process, origin node N₀ communicates subfiles F₁, F₂, F₃, . . . , F_(k−1), F_(k) to recipient nodes N₁, N₂, N₃, . . . , N_(k−1), N_(k), respectively, via concurrent communication paths. As shown in FIG. 7, origin node N₀ has a communication connection to recipient node N₁ for communicating subfile F₁ thereto. And, in accordance with the collection process, node N₁ communicates subfile F₁ to the other recipient nodes N₂, N₃, . . . , N_(k−1), N_(k) of replication group Ĝ₁, respectively, via concurrent communication paths. Thus, node N₁ may begin communicating a portion of subfile F₁ to the other recipient nodes N₂, N₃, . . . , N_(k−1), N_(k) of replication group Ĝ₁ before node N₁ receives all of subfile F₁ from origin node N₀. For instance, node N₁ may communicate packets of subfile F₁ to the other recipient nodes N₂, N₃, . . . , N_(k−1), N_(k) of replication group Ĝ₁ as such packets of subfile F₁ are received by node N₁ from origin node N₀, rather than waiting for the receipt of all packets of subfile F₁ for commencing the communication to the other recipient nodes N₂, N₃, . . . , N_(k−1), N_(k).

Of course, also in the collection step, node N₁ may simultaneously have k−1 concurrent communication paths established with recipient nodes N₂, N₃, . . . , N_(k−1), N_(k) for receiving subfiles F₂, F₃, . . . , F_(k−1), F_(k) from those recipient nodes (not shown in FIG. 7 for simplicity). For instance, each of the other recipient nodes N₂, N₃, . . . , N_(k−1), N_(k) of replication group Ĝ₁ may begin communicating a portion of their respective subfiles that they are receiving from origin node N₀ to node N₁ before the other recipient nodes receive all of their respective subfile from origin node N₀. For instance, node N₂ may communicate packets of subfile F₂ to the other recipient nodes N₁, N₃, . . . , N_(k−1), N_(k) of replication group Ĝ₁ as such packets of subfile F₂ are received by node N₂ from origin node N₀, rather than waiting for the receipt of all packets of subfile F₂ for commencing the communication to the other recipient nodes N₁, N₃, . . . , N_(k−1), N_(k).

Accordingly, each of the recipient nodes N₁, N₂, N₃, . . . , N_(k−1), N_(k) of replication group Ĝ₁ may concurrently have a communication path established with origin node N₀ for receiving a corresponding one of subfiles F₁, F₂, F₃, . . . , F_(k−1), F_(k) therefrom; each of the recipient nodes N₁, N₂, N₃, . . . , N_(k−1), N_(k) of replication group Ĝ₁ may have k−1 concurrent communication paths established with the other remaining recipient nodes for communicating its respective subfile that it receives from origin node N₀ to the remaining recipient nodes; and each of the recipient nodes N₁, N₂, N₃, . . . , N_(k−1), N_(k) of replication group Ĝ₁ may simultaneously have k−1 concurrent communication paths established with the other remaining recipient nodes for receiving subfiles from those remaining recipient nodes.

In certain embodiments, k corresponds to the maximum concurrent connections supportable by each recipient node N₁, . . . , N_(k). Further, if the total number n of recipient nodes to which file F is to be distributed is greater than k, then the nodes may be logically organized into a plurality of replication groups each having k nodes. In such case, after recipient node N₁ of group Ĝ₁ receives its entire subfile F₁ from origin node N₀, the communication connection with node N₀ may be terminated and a connection with a recipient node of a different replication group may be established, such as with node N₁ ^(G) ¹ ¹ of replication group G₁ ¹ shown in the example of FIG. 7. For instance, after each node N_(i) of group Ĝ₁ receives its entire subfile F_(i) from origin node N₀, its communication connection with node N₀ may be terminated and a replaced with a connection with a corresponding recipient node of a different replication group, such as with node N_(i) ^(G) ¹ ₁ of replication group G₁ ¹ shown in the example of FIG. 7. The recipient nodes of such different replication group may follow a fast-forward mode of distributing among themselves their respective subfiles that they are receiving from the nodes of replication group G₁.

In certain embodiments, k+1 corresponds to the maximum concurrent connections supportable by each recipient node N₁, . . . , N_(k). Further, if the total number n of recipient nodes to which file F is to be distributed is greater than k, then the nodes may be logically organized into a plurality of replication groups each having k nodes. As described above with FIG. 4, the plurality of replication groups may be logically organized into a primary multicast tree, and in certain embodiments the logical organization may further include secondary multicast tree(s). As an example of this embodiment, each recipient node of replication group Ĝ₁ may establish a concurrent communication connection with a corresponding recipient node of a different replication group, such as with replication group Ĝ₂ of FIG. 7 (see also FIG. 4) and begin communicating the subfile that it receives from origin node N₀ before such subfile is fully received from origin node N₀.

An example of this embodiment is shown for node N₁ in FIG. 5. As described above, recipient node N₁ of replication group Ĝ₁ may concurrently have: 1) a communication path established with origin node N₀ for receiving subfile F₁ therefrom, 2) k−1 concurrent communication paths established with the other remaining recipient nodes N₂, N₃, . . . , N_(k−1), N_(k) of group Ĝ₁ for communicating its respective subfile F₁ that it receives from origin node N₀ to the remaining recipient nodes, and 3) k−1 concurrent communication paths established with the other remaining recipient nodes N₂, N₃, . . . , N_(k−1), N_(k) for receiving the respective subfiles F₁, . . . , F_(k) from those remaining recipient nodes. Additionally, node N, may concurrently have a communication connection to a node of another replication group, such as node N₁ ² of group G₂ in FIG. 7. Thus, node N₁ may begin communicating subfile F, to node N₁ ² of group Ĝ₂ before node N₁ receives the full subfile F₁ from origin node N₀. As described above, group Ĝ₂ may be referred to herein as being a group within a primary multicast tree, such as primary multicast tree {circumflex over (M)} of FIG. 4. After node N₁ fully receives subfile F₁ from origin node N0, it may terminate its communication connection with origin node N0 and replace it with a communication connection to a node of another replication group, such as node N_(i) ^(G) ¹ ₁ of replication group G₁ ¹ shown in the example of FIG. 7. As described above, group G₁ ¹ may be referred to herein as being a group within a secondary multicast tree, such as within secondary multicast tree M¹ of FIG. 4.

In certain embodiments, k+2 corresponds to the maximum concurrent connections supportable by each recipient node N₁, . . . , N_(k). Further, if the total number n of recipient nodes to which file F is to be distributed is greater than k, then the nodes may be logically organized into a plurality of replication groups each having k nodes. In such case, each node of replication group Ĝ₁ may establish a concurrent communication connection with each of the other recipient nodes of such replication group Ĝ₁, as well as with a recipient node of each of two different replication groups of the primary multicast tree. For instance, in the example shown in FIG. 7 for node N₁, such recipient node N, of replication group Ĝ₁ may concurrently have: 1) a communication path established with origin node N₀ for receiving subfile F₁ therefrom, 2) k−1 concurrent communication paths established with the other remaining recipient nodes N₂, N₃, . . . , N_(k−1), N_(k) of group Ĝ₁ for communicating its respective subfile F₁ that it receives from origin node N₀ to the remaining recipient nodes, and 3) k−1 concurrent communication paths established with the other remaining recipient nodes N₂, N₃, . . . , N_(k−1), N_(k) for receiving the respective subfiles F₁, . . . , F_(k) from those remaining recipient nodes. Additionally, node N₁ may concurrently have a communication connection to a node of another replication group, such as node N₁ ² of group Ĝ₂ in FIG. 7. Further, in this example embodiment, node N₁ may concurrently have a communication connection to a node of another replication group of the primary multicast tree (such other node not shown in FIG. 7). Thus, node N₁ may begin communicating subfile F₁ to node N₁ ² of group Ĝ₂, as well as to the corresponding node of another replication group in the primary multicast tree, before node N₁ receives the full subfile F₁ from origin node N₀.

Turning now to FIG. 8, an example-operational flow diagram for distributing a file from an origin node to a plurality of recipient-nodes in accordance with one embodiment of the present invention is shown. In operational block 801, a number of subfiles, into which file F is to be partitioned is determined. For instance, as shown in the example of FIGS. 1-3 above, in certain embodiments a ALM-Fastfeplica technique may be implemented in which file F may be partitioned into a number of subfiles corresponding to the number k of concurrent communication connections supportable by each recipient node. In operational block 802, file F is partitioned into the determined number of subfiles.

In operational block 803, a subfile is distributed from an origin node to each of a plurality of recipient nodes, wherein all of the subfiles comprising file F are distributed from the origin node. However, all of the subfiles are not distributed from the origin node to each of the plurality of recipient nodes. As shown, in certain embodiments block 803 may comprise operational block 803A, wherein a different subfile is distributed to each recipient node within the distribution group, as in the example of FIGS. 1-3 above in which the ALM-FastReplica technique is implemented. That is, each recipient node may receive a unique subfile from the origin node that is not received by any of the other recipient nodes within the distribution group.

In operational block 804, the plurality of recipient nodes exchange their respective subfiles such that each recipient node obtains all of the determined number of subfiles comprising file F. More specifically, as described above, each of the plurality of recipient nodes begins to communicate the subfile that it receives from the origin node to the other recipient nodes before fully receiving such subfile from the origin node.

In operational block 805, scaling operations may be performed, if needed. That is, if the number of recipient nodes is sufficiently large, the distribution process may be scaled to enable distribution to such a large number of recipient nodes. For instance, the distribution technique may be scaled to allow for a file distribution to hundreds, thousands, or tens of thousands, of recipient nodes, for example. More particularly, if it is determined that the number k of concurrent communication connections that can be supported by each of the nodes N_(o), . . . , N_(n) is less than the total number n of recipient nodes n, then the distribution technique may be scaled for distribution to a plurality of groups of recipient nodes as described further below. Various suitable scaling techniques may be utilized. One scaling technique that may be utilized in certain embodiments comprises logically arranging the recipient nodes into a plurality of replication groups, and such replication groups may be logically organized into primary, and in some instances secondary, multicast trees, as described above with FIG. 4.

The ALM-FastReplica distribution technique is further described in concurrently filed and commonly assigned U.S. patent application Ser. No. ______ [Attorney Docket No. 200310234-1] titled “SYSTEM AND METHOD HAVING IMPROVED EFFICIENCY FOR DISTRIBUTING A FILE AMONG A PLURALITY OF RECIPIENTS”, the disclosure of which is hereby incorporated herein by reference.

Embodiments of the present invention improve the robustness (or “reliability”) of the above-described file distribution process (e.g., the ALM-FastReplica algorithm) to deal with node failures. As can be seen from the above description of ALM-FastReplica, for example, such ALM-FastReplica algorithm is sensitive to node failures. For example, if node N_(i) fails during the collection step shown in FIGS. 2 and 3, this event may impact all other nodes N₂, . . . , N_(k) in this distribution group because each node depends on node N₁ to receive subfile F₁. A similar situation occurs in the example scaled ALM-FastReplica algorithm described above (e.g., as shown in FIG. 4-6), where a failure of node N_(i) during a file replication may impact all the nodes in the dependent groups of a primary and/or secondary multicast tree because the nodes in such groups should receive subfile F_(i) from node N_(i). For example, if node if node N₁ ¹ (from group Ĝ₁ in primary multicast tree {circumflex over (M)} of FIG. 4) fails during either the distribution or collection steps, then this event may impact all nodes N₂ ¹, . . . , N_(k) ¹ in the group Ĝ₁ because each node depends on node N₁ ¹ to replicate subfile F_(l). A similar situation occurs if a failure of node N_(i) ¹ occurs during the group communication step between groups Ĝ₁ and Ĝ₂ of primary multicast tree {circumflex over (M)} this failure may impact all the nodes in the dependent subtree, i.e., all groups in the primary multicast tree {circumflex over (M)} following group Ĝ₁ (such as groups Ĝ₂-Ĝ_(m) shown in FIG. 4), because the nodes in this subtree should receive subfile F_(i) from node N_(i) ¹.

An embodiment of the present invention provides a reliable distribution technique (such as the above-described ALM-FastReplica distribution technique) that efficiently deals with node failures by making a local “repair decision” (which may be referred to herein as a local “distribution detour decision”) within the particular group of nodes. As described below, an embodiment of the present invention, keeps the main structure of the ALM-FastReplica algorithm described above practically unchanged, while adding the desired property of resilience to node failures.

As an example of one embodiment, consider the nodes comprising group Ĝ₁ in the example discussed above in conjunction with FIG. 4. Such group Ĝ₁ is referred to herein as an initial group. In this example embodiment, special attention is paid to group Ĝ₁ and node failures in it. Nodes of group Ĝ₁ are referred to herein as initial nodes. The rest of the groups are referred to as subsequent groups, and their nodes are referred to as subsequent nodes.

There are several communication patterns in which a node N_(i) ^(j) might be involved in the ALM-FastReplica distribution technique at a moment of its failure. If node N_(i) ^(j) is an initial node (i.e., is a node of group Ĝ₁ in this example, such that N_(i) ^(j)=N_(i) ¹), it may fail during any of the following:

1. Node N_(i) ¹ of group Ĝ₁ may fail during the distribution step while (or before) node N₀ is communicating subfile F_(i) to node N_(i) ¹. Only node N₀ has subfile F_(i) at this point (none of the nodes in group Ĝ₁ has received this subfile F_(i) yet). Since node N_(i) ¹ is failed during (or before) the communication of subfile F_(i) from N₀ to node N_(i) ¹, node N₀ is aware of node N_(i) ¹'s failure. For instance, node N₀ may receive an error message (e.g., it will get no “ACK” for sent packets and eventually a TCP timeout may be encountered) when attempting to communicate the subfile F_(i) to node N_(i) ¹ indicating to node N₀ that the communication of subfile F_(i) to node N_(i) ¹ was unsuccessful.

2. Node N_(i) ¹ may fail during the collection step, when node N_(i) ¹ has received a portion (e.g., the first bytes) of subfile F_(i) and started to communicate it to the remaining nodes in group Ĝ₁.

3. Node N_(i) ¹ may fail during the group communication step in the primary multicast tree {circumflex over (M)}. That is, node N_(i) ¹ may fail when it is communicating subfile F_(i) to node N_(i) ² of group Ĝ₂.

4. Node N_(i) ¹ may fail during the group communication step in the secondary multicast tree M¹. That is, node N_(i) ¹ may fail when it is communicating subfile F_(i) to node N_(i) ^(G) ¹ ¹ of group G₁ ¹. The crucial difference of node N_(i) ¹'s failure at this step is that any node in group Ĝ₁ already has the entire file F, and in particular, the subfile F_(i), at this point.

According to one embodiment of the present invention, the nodes within each distribution group G_(j)={N_(l) ^(j), . . . , N_(k) ^(j)} exchange heartbeat messages. Further, according to this embodiment of the present invention, node N_(i) ^(j) of group G_(j) sends heartbeat messages to node N_(i) ^(j−1) of group G_(j−1). That is, each node of a distribution group may send heartbeat messages to a corresponding node of an earlier distribution group in the distribution tree (e.g., in the primary and/or secondary multicast tree). For instance, node N_(i) ^(j) of a distribution group G_(j) may send heartbeat messages to a corresponding node N_(i) ^(j−1) of an earlier distribution group G_(j−1) from which node N_(i) ^(j) is to receive subfile F_(i) in accordance with the ALM-FastReplica distribution technique described above. Such heartbeat messages nay be augmented with additional information on the corresponding algorithm step(s) and the current replication list of nodes corresponding to the identified algorithm step(s).

It should be recognized that because the ALM-FastReplica technique may perform distribution, collection, and group communication steps concurrently, as described above, a node may be involved with a plurality of such steps at the time of any given hearbeat. Table 1 shows an example heartbeat message that may be communicated by node N₁ ¹. As shown in the example of Table 1, node N₁ ¹ is involved with both collection and group communication steps at the time of this example heartbeat message. Thus, in this example, the origin node N₀ has completed its distribution of subfile F_(i) to node N₁ ¹ and such node N₁ ¹ is completing its collection and group communication steps of the above-described ALM-FastReplica technique. The distribution list identifies nodes {N₂ ¹, . . . , N_(k) ¹} with which node N₁ ¹ is performing the collection step, and node {N₁ ²} with which node N₁ ¹ is performing the group communication step in this example. TABLE 1 Current Replication Current Node Identification Node Status Step(s) Distribution List N₁ ¹ I'm Alive Collection; and Nodes Group {N₂ ¹, . . . ,N_(k) ¹}, Communication and {N₁ ²}

The information about the corresponding algorithm step currently being performed by a particular node in a group is included in the heartbeat message because of the asynchronous nature of the above-described ALM-FastReplica algorithm. For example, while some of the nodes of group Ĝ₁ may be performing file distribution in the primary multicast tree {circumflex over (M)} (i.e., they are still replicating their respective subfiles received from origin node N₀ to the other nodes of group Ĝ₁ and/or to corresponding nodes of group Ĝ₂ of the primary multicast tree), some other “faster” nodes of the same group G₁ ¹ might already have started performing file distribution in a secondary multicast tree M¹ (i.e., they are replicating their respective subfiles to the corresponding nodes of group G₁ ¹ of the secondary multicast tree M¹ as shown in the example of FIG. 4).

Thus in case of node failure, it is desirable to know:

-   -   (a) which particular node in the group has failed;     -   (b) whether the node is an initial node;     -   (c) whether the corresponding step(s) of the algorithm for which         the failed node is currently responsible for performing is/are         distribution, collection, and/or group communication step(s);         and     -   (d) which multicast tree, group, and set of receiving nodes is         impacted as a result of this failure.

According to an embodiment of the present invention, a different “repair procedure” may be utilized depending on the circumstances under which the node failure occurred (e.g., whether the failed node is an initial node currently responsible for performing the distribution, collection, and/or group communication steps in a primary multicast tree of the ALM-FastReplica algorithm, or whether the failed node fails during the group communication step wherein the failed node is either a subsequent node or an initial node performing the group communication step to a secondary multicast tree of the ALM-FastReplica algorithm). First, consider when an initial node N_(i) ¹ of group Ĝ₁ fails during distribution, collection, and/or group communication step(s) in a primary multicast tree {circumflex over (M)} of the above-described ALM-FastReplica algorithm. In this case, origin node N₀ is either aware of node N_(i) ¹'s failure (because it received an error message when attempting to communicate the subfile F_(i) to node N_(i) ¹ indicating to node N₀ that the communication of subfile F_(i) to node N_(i) ¹ was unsuccessful) or receives a message about this failure from the heartbeat group Ĝ₁. An example of a node failure under these circumstances is described further below in conjunction with FIGS. 9-10C.

An example of such a node failure during the distribution step and an example technique for “repairing” the distribution of file F to the nodes of the distribution group is shown in FIG. 9. More specifically, FIG. 9 shows an example in which origin node N₀ is distributing subfiles {F₁, . . . , F_(k)} to recipient nodes {N₁ ¹, . . . , N_(k) ¹} of group Ĝ₁ of primary multicast tree {circumflex over (M)}. In the example of FIG. 9, node N₃ ¹ has failed. Accordingly, origin node N₀ is unable to communicate subfile F₃ to node N₃ ¹. At the time of failure of node N₃ ¹, it may be involved with the distribution step (receiving subfile F₃ from origin node N₀), and it may also concurrently be involved with performance of the collection step, (communicating received portions of subfile F₃ to the other nodes of group Ĝ₁) and/or performance of a group communication (communicating received portions of subtile F₃ to a corresponding node N₃ ² of group Ĝ₂) as described above for the ALM-FastReplica distribution algorithm.

In this example, origin node N₀ is either aware of node N₃ ¹'s failure (because origin node N₀ received an error message when attempting to communicate the subfile F₃ to node N₃ ¹ indicating to node N₀ that the communication of subfile F₃ to node N₃ ¹ was unsuccessful) or origin node N₀ receives a message about this failure from the heartbeat group Ĝ₁. Because origin node N₀ is the root of the overall replication procedure in this example, to avoid a single point of failure it may be implemented having a “buddy-node” {circumflex over (N)}₀ with mirrored information and data in certain embodiments, as shown in FIG. 9. In such an implementation, node N₀ may send a message to mirrored node {circumflex over (N)}₀ to open k−1 network connections to the rest of the nodes in group Ĝ₁ for sending the missing subfile F₃ to each node in that group. Thus, as shown in the example of FIG. 9, mirrored (or “buddy”) node {circumflex over (N)}₀ may perform the following “repair” step (or “distribution detour”): it establishes k−1 communication connections to the rest of the nodes in group Ĝ₁ (i.e., the non-failed nodes {N₁ ¹, N₂ ¹, and, N₄ ¹, . . . , N_(k) ¹}) to send the missing F₃ subfile to each such non-failed node in group Ĝ₁. Further, as also shown in FIG. 9, mirrored node {circumflex over (N)}0 may establish a communication connection with node N₃ ² of group Ĝ₂ to which failed node N₃ ¹ is responsible for distributing subfile F₃ through the group communication step of the above-described ALM-FastReplica algorithm, and mirrored node {circumflex over (N)}₀ may use such communication connection to communicate subfile F₃ to node N₃ ². It should be recognized that buddy node {circumflex over (N)}₀ may distribute subfile F₃ to each non-failed node in group Ĝ₁ and to node N₃ ² of group Ĝ₂ concurrently with origin node N₀ performing distribution to the non-failed nodes of group Ĝ₁.

The process of enabling reliable distribution to non-failed nodes even when a failed node exists in a distribution group may be referred to as a “repair” of the distribution. Although, the failed node itself is not repaired by this process (but may instead remain in a failed state). Thus, the use of “repair” herein should not be confused with repairing an actual failed node, but is instead used as repairing a distribution process that is dependent on a failed node. This process may instead be referred to herein as a “detoured” distribution process. For instance, in the above example the subfile F₃ is distributed to the non-failed nodes via a detour around the failed node N₃ ¹.

Thus, after the above-described detouring of the distribution and group communication steps of FIG. 9, each of the non-failed nodes in group Ĝ₁ has all of the subfiles of original file F. Further, node N₃ ² of group Ĝ₂ receives subfile F₃.

Consider instead now that a node failure occurs for an initial node (of group Ĝ₁) after such node has fully received its respective subfile from the origin node but before it has forwarded all of such subfile on to the other nodes of the group. An example of such a node failure under these circumstances and an example technique for “repairing” the replication of file P to the nodes of the replication group is shown in FIGS. 10A-10C. More specifically, FIG. 10A shows an example in which the nodes of group Ĝ₁ have each fully received their respective, subfiles from origin node N₀ and are completing the collection step of the ALM-FastReplica algorithm by communicating the final portions of their respective subfiles to each of the other nodes of the group. For instance, as shown in the example of FIG. 10A, all of the non-failed nodes are communicating the final portions of their respective subfiles to node N₁ ¹. Of course, while not shown in FIG. 10A for conciseness, each of the non-failed nodes may have concurrent communication connections with each of the other non-failed nodes to concurrently exchange their respective subfiles.

In the example of FIG. 10A, node N₃ ¹ has failed. In this case, node N₃ ¹ failed after the subfile F₃ was fully distributed to such node N₃ ¹ from origin node N₀. Thus, node N₃ ¹ has the entire subfile F₃ stored thereto and has terminated its communication connection with origin node N₀, but is unable to communicate such subfile F₃ to the other recipient nodes of group Ĝ₁. In this case, node N₀ is unaware of node N₃ ¹'s failure because the communication of subfile F₃ to node N₃ ¹ has completed before node N₃ ¹ fails.

According to one embodiment of the present invention, heartbeat messages are used between the nodes of a distribution group (e.g., group Ĝ₁ in the above example) to detect when one of the nodes fails. For instance, using the heartbeat messages of one embodiment, the failure of node N₃ ¹ is detected by nodes within group Ĝ₁, and this information is sent to origin node N₀. For example, each node of group Ĝ₁ may periodically send a heartbeat message to origin node N₀, such as the example heartbeat message of Table 1, as shown in FIG. 10B. For instance, in the example of FIG. 10B, nodes {N₁ ¹, N₂ ¹, and N₄ ¹, . . . , N_(k) ¹} send heartbeat messages {HB−N₁ ¹, HB−N₂ ^(i), and HB−N₄ ¹, . . . , HB−N_(k) ¹}, respectively, to node N₀. Upon node N₀ recognizing that a heartbeat message is not received from node N₃ ¹, node N₀ detects that node N₃ ¹ has failed. As another example, in addition to or rather than the recipient nodes of group Ĝ₁ periodically sending heartbeat messages to their origin node N₀, such recipient nodes may exchange heartbeat messages with each other. For instance, the recipient nodes of a group (e.g., Ĝ₁) may exchange heartbeat messages with each other, and upon a recipient node detecting that another node of the group has failed (e.g., which may be detected by a heartbeat message from the failed node not being received in a given time frame) the detecting recipient node may notify the origin node of the failed node's failure.

Once origin node N₀ detects a failed node (e.g., is notified of a node's failure by another recipient node in the group), in one embodiment of the present invention origin node N₀ triggers its buddy node {circumflex over (N)}₀ to perform the following “repair” step (or “distribution detour”): it opens connections to the impacted nodes in group Ĝ₁ and Ĝ₂ to send missing subfile F₃ to such nodes, as shown in FIG. 10C. For instance, buddy node {circumflex over (N)}₀ opens communication connections with nodes {N₁ ¹, N₂ ¹, and N₄ ¹, . . . , N_(k) ¹} of group Ĝ₁ to send subfile F₃ thereto, and it opens a communication connection to node N₃ ² of group Ĝ₂ to send subfile F₃ thereto.

Thus, after the above-described detoured distribution step of FIG. 10C, each of the non-failed nodes in group Ĝ₁ has all of the subfiles of original file F. Further, node N₃ ² of group Ĝ₂ receives subfile F₃.

It should be recognized that the exchange of heartbeat messages by a “group” of nodes may be performed only during the distribution process in certain embodiments. For instance, recipient nodes may be logically “grouped” only for a distribution of a file F, and different distributions (of other files at other times) may comprise different logical groupings of the recipient nodes. Thus, the recipient nodes may exchange heartbeat messages with the other nodes of their group only during a distribution process, and once the distribution is complete, the nodes may no longer be “grouped” or exchange heartbeat messages.

Now consider a node failure occurring during the group communication step wherein the failed node is either: 1) a subsequent node, or 2) an initial node performing the group communication step to a secondary multicast tree of the ALM-FastReplica algorithm. An example of such a node failure under these circumstances and an example technique for “repairing” the replication of file F to the nodes of the replication group is shown in FIGS. 11A-11B. FIG. 11A shows an example of a failed subsequent node N_(i) ^(j) in group G_(j) while it was communicating subfile F_(i) to the rest of the nodes in group G_(j) (i.e., performing a collection step) and further to node N_(i) ^(j+1) of group G_(j+1) during the group communication step of the example ALM-FastReplica algorithm. Thus, in this example, groups G_(j−1), G_(j), and G_(j+1) are groups in a primary multicast tree.

An example repair procedure for node N_(i) ^(j) of the example of FIG. 11A is shown in FIG. 11B. As shown, once node N_(i) ^(j−1) realizes that node N_(i) ^(j) has failed, node N_(i) ^(j−1) conveys this information to the rest of the nodes in group G_(j−1). The nodes in group G_(j−1) share the additional load of communicating subfile F_(i) to the nodes of group G_(j), as shown in FIG. 11B. For instance, each of the nodes of group G_(j−1) communicate subfile F_(i) to a corresponding node of group G_(j), as shown in FIG. 11B. Additionally, node N_(i) ^(j−1) communicates subfile F_(i) to node N_(i) ^(j+1) of group G_(j+1). That is, node N_(i) ^(j−1) effectively substitutes for failed node N_(i) ^(j) to communicate subfile F_(i) to the corresponding node N_(i) ^(j+1) of the next group (group G_(j+1) in this example) of the primary multicast tree.

The distribution lists are the same for all the nodes of group G_(j), and after the “repair” step, the ALM-FastReplica algorithm proceeds in the usual way for the entire subtree originated in group G_(j). In view of the above, the nodes in group G_(j−1) share the additional load of transferring file F_(i) to the next, secondary multicast tree of group G^(j). Since the load of failed node N_(i) ^(j) is shared among k nodes of group G_(j−1) the performance degradation is gradual for the repaired portion of the distribution tree.

Now consider a node failure occurring during the group communication step wherein the failed node is an initial node performing the group communication step to a secondary multicast tree of the ALM-FastReplica algorithm. This case is similar to that of FIGS. 11A-11B, wherein groups G_(j-1) and G_(j) are groups in a primary multicast tree and group G_(j+1) is a group in a secondary multicast tree to which group G_(j) distributes file F. As described above, in the ALM-FastReplica algorithm after fully receiving subfile F_(i) from node N_(i) ^(j−1), node N_(i) ^(j) of group G_(j) may terminate its communication connection with node N_(i) ^(j−1) and begin communicating subfile F_(i) to node N_(i) ^(j+1) of group G_(j+1) of a secondary multicast tree. Suppose that node N_(i) ^(j) fails, as shown in FIG. 11A, after it fully receives subfile F_(i) from node N_(i) ^(j−1) but before it fully communicates such subfile F_(i) to node N_(i) ^(j+1) of group G_(j+1) of a secondary multicast tree. The example repair procedure for node N_(i) ^(j) shown in FIG. 11B may be utilized in certain embodiments. More specifically, heartbeat messages may be exchanged between the nodes of group G_(j), as described above, and upon a node detecting the failure of node N_(i) ^(j), it may notify node N_(i) ^(j−1) and node N_(i) ^(j−1) may effectively substitute for failed node N_(i) ^(j) to communicate subfile F_(i) to the corresponding node N_(i) ^(j+1) of group G_(j+1) of the secondary multicast tree. In certain embodiments, heartbeat messages are exchanged between the nodes of “vertical” (or consecutive) groups within a multicast tree, such as between groups G_(j) and group G_(j−1), and upon node N_(i) ^(j−1) detecting the failure of node N_(i) ^(j) it may effectively substitute for the failed node to communicate subfile F_(i) to the corresponding node N_(i) ^(j+1) of group G_(j+1) of the secondary multicast tree, as described above.

Turning to FIGS. 12A-12B, an example operational flow diagram is shown for a repair procedure for the above-described ALM-FastReplica distribution process in accordance with an embodiment of the present invention. As shown in FIG. 12A, operation of this example embodiment starts with operational block 1201, whereat it is determined whether any nodes involved in the distribution process have failed. As described above, during the distribution process a recipient node may be detected as having failed in a number of different ways including, as examples, through the exchange of heartbeat messages and/or through a failed communication with a node (e.g., origin node) attempting to distribute a subfile to the failed node. If a node is not detected as failed, the repair procedure waits at block 1201 (while the distribution process continues as described above).

If, during the distribution process, a node N_(i) ^(j) is detected in block 1201 as failed, operation advances to block 1202 whereat a determination is made as to whether the failed node N_(i) ^(j) is an initial node. That is, a determination is made as to whether node N_(i) ^(j) is node N_(i) ¹ of group Ĝ₁ of primary multicast tree {circumflex over (M)} in the example of FIG. 4. If node N_(i) ^(j) is an initial node, then operation advances to block 1203 where a determination is made as to whether the failed node N_(i) ¹ is currently responsible for performing a group communication step of the ALM-FastReplica algorithm to group G₁ ¹ of secondary multicast tree M¹ in the example of FIG. 4. If the failed node N_(i) ¹ is currently responsible for performing such a group communication to group G₁ ¹ of secondary multicast tree M¹, operation advances to block 1204 whereat origin node N₀ is notified of node N_(i) ¹'s failure. That is, as described above, node N_(i) ¹ begins to perform group communication to group G₁ ¹ of secondary multicast tree M¹ after it has fully received subfile F_(i) and has terminated its communication connection with origin node N₀. Thus, origin node N₀ may be unaware of node N_(i) ¹'s failure, and through exchanging heartbeat messages another node in group Ĝ₁ may detect node N_(i) ¹'s failure and notify origin node N₀. In certain embodiments, heartbeat messages may be sent from recipient nodes {N₁ ¹, . . . , N_(k) ¹} of group Ĝ₁ to origin node N₀ until completion of the file distribution (or at least until completion of the portion of the distribution process involving group Ĝ₁), and such heartbeat messages may enable origin node N₀ to detect a failure of a node in group Ĝ₁.

In operational block 1205, origin node N₀ triggers its buddy node {circumflex over (N)}₀ to establish a communication connection to node N_(i) ¹ of group G₁ ¹ of secondary multicast tree M¹, and buddy node {circumflex over (N)}₀ communicates subfile F_(i) to such node N_(i) ¹ of group G₁ ¹. That is, buddy node {circumflex over (N)}₀ effectively substitutes for failed node N_(i) ¹ of group Ĝ₁ to communicate subfile F_(i) to node G₁ ¹ of secondary multicast tree M¹. In alternative embodiments, origin node N₀ may itself substitute for failed node N_(i) ¹ of group Ĝ₁ to communicate subfile F_(i) to node G₁ ¹ of secondary multicast tree M¹.

If in block 1203 it is determined that the failed node N_(i) ¹ is not currently responsible for performing group communication to group G₁ ¹ of secondary multicast tree M¹, then operation advances to block 1206. At block 1206 buddy node {circumflex over (N)}₀ establishes a communication connection with the non-failed nodes of group Ĝ₁. Operation then advances to block 1207 whereat buddy node {circumflex over (N)}₀ communicates subfile F_(i) to whatever nodes of groups Ĝ₁ and Ĝ₂ to which subfile F_(i) has not yet been fully distributed. For instance, buddy node {circumflex over (N)}₀ may communicate subfile F_(i) to the non-failed nodes of group Ĝ₁ that have not yet received subfile F_(i). Further, if failed node N_(i) ¹ is responsible for performing group communication to group Ĝ₂ of primary multicast tree {circumflex over (M)}, buddy node {circumflex over (N)}₀ may establish a communication connection with node N_(i) ² of such group Ĝ₂ and communicates subfile F_(i) thereto in block 1208.

If it is determined in block 1202 that the failed node N₁ ^(j) is not an initial node (and is therefore a subsequent node), operation advances (via connector “A”) to block 1209 shown in FIG. 12B. In block 1209, node N_(i) ^(j−1) detects that node N_(i) ^(j) has failed (e.g., through a failed communication attempt therewith or through notification from a node in the heartbeat group with node N_(i) ^(j)). In block 1210, node N_(i) ^(j−1) informs the rest of the nodes in group G_(j−1) of node N_(i) ^(j)'s failure. In block 1211, the nodes of group G_(j−1) share the additional load of communicating subfile F_(i) to the nodes of group G_(j), as shown in FIG. 11B. For instance, each of the nodes of group G_(j−1) communicate subfile F_(i) to a corresponding node of group G_(j), as shown in FIG. 11B. Additionally, if failed node N_(i) ^(j) is responsible for performing group communication to a next group G_(j+1), node N_(i) ^(j−1) communicates subfile Fi to node N_(i) ^(j+1) of such next group G_(j+1) in operational block 1212. That is, node N_(i) ^(j−1) effectively substitutes for failed node N_(i) ^(j) to communicate subfile F_(i) to the corresponding node N_(i) ^(j+1) of the next group (group G_(j+1) in this example).

While FIGS. 12A-12B show one example of a repair process that enables reliable distribution of file F accounting for failed recipient nodes, various other repair procedures may be utilized in accordance with the distribution techniques described herein, and any such repair procedures are intended to be within the scope of the present invention.

As one example application of embodiments of the present invention, consider the distribution of streaming media files within a CDN. In order to improve streaming media quality, the latest work in this direction proposes to stream video from multiple edge servers (or mirror sites), and in particular, by combining the benefits of multiple description coding (MDC) with Internet path diversity. MDC codes a media stream into multiple complementary descriptions. These descriptions have the property that if either description is received it can be used to decode the baseline quality video, and multiple descriptions can be used to decode improved quality video.

Thus, for a media file encoded with MDC, different descriptions can be treated as subfiles, and a distribution technique, such as the above-described ALM-FastReplica technique, can be applied to replicate them. That is, while the above examples describe partitioning a file into subfiles based, for example, on the number k of concurrent communication connections that can be supported by a node, in certain embodiments the distribution technique may be utilized with a file F encoded with multiple descriptions, wherein each of the multiple descriptions may be distributed to recipient nodes in the manner in which the above-described subfiles of a file F are described as being distributed.

Taking into account the nature of MDC (i.e., that either description received by the recipient node can be used to decode the baseline quality video), the reliability of the ALM-FastReplica algorithm may be improved. For instance, when using primary and secondary multicast trees as described above in FIG. 4 for distributing a media file encoded with MDC, even if failed nodes exist in the primary and/or secondary multicast trees, this ALM-FastReplica technique may provide a suitable distribution technique because receipt by nodes below the failed node(s) in the distribution tree of a portion of the descriptions (from the working nodes of the higher level) will be enough to decode the good quality video.

Various elements for performing the above-described file distribution and repair functions of embodiments of the present invention may be implemented in software, hardware, firmware, or a combination thereof. For example, software may be used on an origin node N₀ for determining logical groupings of recipient nodes and/or for partitioning file F into the appropriate number of subfiles. As another example, network interfaces may be used to concurrently communicate sub files from an origin node to recipient nodes of a distribution group (e.g., in the distribution step of ALM-FastReplica), as well as for communication of such subfiles between recipient nodes of the distribution group (e.g., in the collection step of ALM-FastReplica).

When implemented via computer-executable instructions, various elements of embodiments of the present invention for distributing file F from an origin node to recipient nodes are in essence the software code defining the operations of such various elements. The executable instructions or software code may be obtained from a readable medium (e.g., a hard drive media, optical media, EPROM, EEPROM, tape media, cartridge media, flash memory, ROM, memory stick, and/or the like) or communicated via a data signal from a communication medium (e.g., the Internet). In fact, readable media can include any medium that can store or transfer information. 

1. A method of distributing a file from a first node to a plurality of recipient nodes, the method comprising: partitioning a file F into a plurality of subfiles; performing distribution of said file F to a plurality of recipient nodes using a distribution technique that comprises (a) attempting to distribute the plurality of subfiles from a first node to a first group of recipient nodes, wherein the first node attempts to communicate at least one subfile to each recipient node of said first group but not all of said plurality of subfiles to any recipient node of said first group, and (b) said plurality of recipient nodes of said first group attempting to exchange their respective subfiles received from said first node, wherein at least one recipient node of said first group begins communicating a portion of its respective subfile that it is receiving from the first node to at least one other recipient node of said first group before the at least one recipient node fully receives its respective subfile; detecting a failed node of said plurality of recipient nodes; and said distribution technique adapting to distribute all of the subfiles of said file F to each non-failed node of said plurality of recipient nodes.
 2. The method of claim 1 wherein said distribution technique adapting responsive to said detecting a failed node.
 3. The method of claim 1 wherein said attempting to distribute the plurality of subfiles from a first node to a first group of recipient nodes comprises: attempting to distribute a different subfile from said first node to each of said recipient nodes of said first group.
 4. The method of claim 1 wherein said attempting to distribute the plurality of subfiles from a first node to a first group of recipient nodes comprises: attempting to distribute the plurality of subfiles from said first node to said plurality of recipient nodes of said first group concurrently.
 5. The method of claim 1 wherein said plurality of recipient nodes of said first group attempting to exchange their respective subfiles further comprises: each of said plurality of recipient nodes attempting to establishing concurrent communication connections to every other recipient node of said first group.
 6. The method of claim 1 wherein said detecting a failed node comprises said first node detecting a failed node in said first group such that said-first node is unable to communicate a particular subfile to such failed node.
 7. The method of claim 6 wherein said attempting to distribute the plurality of subfiles from a first node to a first group of recipient nodes comprises said first node attempting to establish concurrent communication connections to the recipient nodes of said first group, and wherein said distribution technique adapting comprises: responsive to said first node detecting a failed node in said first group such that said first node is unable to communicate a particular subfile to such failed node, said first node using its established concurrent communication connections with non-failed nodes of said first group to communicate the particular subfile to said non-failed nodes.
 8. The method of claim 6 wherein said attempting to distribute the plurality of subfiles from a first node to a first group of recipient nodes comprises said first node attempting to establish concurrent communication connections to the recipient nodes of said first group, and wherein said distribution technique adapting comprises: responsive to said first node detecting a failed node in said first group such that said first node is unable to communicate a particular subfile to such failed node, said first node triggering a mirror node to establish concurrent communication connections with non-failed nodes of said first group to communicate the particular subfile to said non-failed nodes.
 9. The method of claim 1 wherein said detecting a failed node comprises: said recipient nodes of said first group exchanging heartbeat messages; at least one recipient node of said first group detecting a failed node from analysis of heartbeat messages received; and said at least one recipient node of said first group notifying said first node of said detected failed node.
 10. The method of claim 1 wherein said detecting a failed node comprises: said non-failed recipient nodes of said first group sending heartbeat messages to said first node; and said first node detecting a failed node from analysis of received heartbeat messages from said non-failed recipient nodes.
 11. The method of claim 1 further comprising: said first group of recipient nodes attempting to communicate said file F to a second group comprising a plurality of recipient nodes.
 12. The method of claim 1I further comprising: each recipient node of said first group attempting to communicate a subfile to at least one recipient node of said second group.
 13. The method of claim 12 further comprising: each recipient node of said first group attempting to communicate the subfile that it received from said first node to a corresponding node of the second group.
 14. The method of claim 12 wherein said detecting a failed node comprises detecting a failed node in said first group when said failed node of said first group is attempting to communicate a subfile to said at least one recipient node of said second group.
 15. The method of claim 14 wherein said distribution technique adapting further comprises: said first node communicating said subfile to said at least one recipient node of said second group.
 16. The method of claim 14 wherein said distribution technique adapting further comprises: said first node triggering a mirror node to communicate the subfile to said at least one recipient node of said second group.
 17. A system comprising: an origin node operable to partition a file F into a plurality of sub files, wherein said plurality of subfiles correspond in number to a number of recipient nodes in a first group to which said file is to be distributed; said origin node operable to attempt to distribute all of said plurality of sub files to said recipient nodes, wherein said origin node attempts to distribute a different one of said plurality of subfiles to each of said recipient nodes; said recipient nodes operable to attempt to exchange their respective subfiles received from said origin node such that each recipient node obtains all of said plurality of subfiles, wherein at least one recipient node of said first group begins communicating a portion of its respective subfile that it is receiving from the origin node to at least one other recipient node of said first group before the at least one recipient node fully receives its respective subfile from the origin node; said origin node operable to detect a failed node in said first group; and said origin node operable to manage distribution of said file F upon detecting a failed node in said first group in a manner such that every non-failed node of said first group receives said file F.
 18. The system of claim 17 wherein each of said recipient nodes are operable to attempt to distribute a subfile being received from said origin node to the others of said recipient nodes of said first group.
 19. The system of claim 17 wherein said origin node is operable to attempt to distribute the plurality of subfiles to said plurality of recipient nodes of said first group concurrently.
 20. The system of claim 17 wherein said said origin node is operable to trigger a mirror node to establish concurrent communication connections with non-failed nodes of said first group to communicate a subfile to said non-failed nodes.
 21. A method of distributing a file from a first node to a plurality of recipient nodes, the method comprising: attempting to distribute a plurality of subfiles that comprise a file F from a first node to a first group comprising a plurality of recipient nodes, wherein the first node attempts to distribute at least one subfile to each recipient node of said first group but not all of said plurality of subfiles are distributed from the first node to any of the recipient nodes of said first group; said plurality of recipient nodes of said first group attempting to exchange their respective sub files, wherein at least one recipient node of said first group begins communicating a portion of its respective subfile that it is receiving, from the first node to at least one other recipient node of said first group before the at least one recipient node fully receives its respective subfile; detecting whether one of said plurality of recipient nodes of said first group has failed; and if a recipient node of said first group has failed, managing the distribution of the plurality of subfiles to detour their distribution around the failed node such that the file F is distributed to each non-failed node of said plurality of recipient nodes.
 22. The method/of claim 21 wherein said attempting to distribute the plurality of subfiles from a first node to a first group of recipient nodes comprises: attempting to distribute a different subfile from said first node to each of said recipient nodes of said first group.
 23. The method of claim 22 wherein said managing the distribution of the plurality of subfiles to detour their distribution around the failed node such that file F is distributed to each non-failed node of said plurality of recipient nodes comprises: said first node communicating to non-failed nodes of said first group a subfile that the first node would communicate to the failed node if the failed node were not failed.
 24. The method of claim 22 wherein said managing the distribution of the plurality of subfiles to detour their distribution around the failed node such that file F is distributed to each non-failed node of said plurality of recipient nodes comprises: said first node triggering a mirror node to communicate to non-failed nodes of said first group a subfile that the first node would communicate to the failed node if the failed node were not failed.
 25. The method of claim 21 wherein said attempting to distribute the plurality of subfiles from a first node to a first group of recipient nodes comprises: attempting to distribute the plurality of subfiles from said first node to said plurality of recipient nodes of said first group concurrently.
 26. The method of claim 21 wherein said plurality of recipient nodes of said first group attempting to exchange their respective subfiles further comprises: each of said plurality of recipient nodes attempting to establishing concurrent communication connections to every other recipient node of said first group.
 27. The method of claim 21 wherein said detecting whether one of said plurality of recipient nodes of said first group has failed comprises: said recipient nodes of said first group exchanging heartbeat messages; at least one recipient node of said first group detecting a failed node from analysis of heartbeat messages received; and said at least one recipient node of said first group notifying said first node of said detected failed node.
 28. The method of claim 21 wherein said detecting whether one of said plurality of recipient nodes of said first group has failed comprises: the non-failed recipient nodes of said first group sending heartbeat messages to said first node; and said first node detecting a failed node from analysis of received heartbeat messages from the non-failed recipient nodes. 